The present invention relates to the field of high frequency modules using millimeter waves or microwaves, and radio apparatuses employing such modules.
One known millimeter waveguide using anisotropically etched silicon substrate is disclosed in IEEE MTT-S Digest pp. 797-800, 1996.
FIG. 10 shows the structure of a conventional millimeter wave transmission line. Silicon dioxide (SiO2) 902 is deposited on a silicon substrate 901, and a microstrip line 903 is formed on the silicon dioxide 902. A shielded microstrip line is created by sandwiching the silicon substrate 901 between a carrier substrate 904 coated with metal film, and another silicon substrate 905 processed by micromachining, to achieve a shielding structure. With this shielding structure, which uses air as the dielectric medium, a transmission line with low loss can be achieved.
In this type of millimeter transmission line, however, modularization by mounting other millimeter wave components such as an MMIC (Monolithic Microwave Integrated Circuit) may be difficult, because the microstrip line is supported by silicon dioxide in midair. There may also be a problem with strength. Two sheets of silicon substrate are processed by micromachining, and an unduly thick silicon dioxide film must be formed to ensure strength. These result in the need for complicated processing during manufacturing.
The present invention offers an inexpensive millimeter wave and microwave apparatus by facilitating processing of a millimeter wave module in which components such as a low-loss filter and MMIC are mounted.
A millimeter wave module of the present invention comprises first and second substrates. The first substrate comprises a cavity on one flat face, a conductor formed on the bottom and side faces of the cavity, a connection part formed on a flat face around the cavity and electrically connected to the conductor formed in the cavity, and an air layer inside the cavity. The second substrate made of dielectrics comprises, on one flat face, metal patterning of a microstrip filter and a connection part connected to the metal patterning. The second substrate is mounted on the first substrate, so that the connection part of the first substrate is attached to the connection part connected to the metal patterning of the second substrate, and that the metal patterning of the second substrate faces the air layer in the cavity of the first substrate and also covers the cavity.
With this configuration, a low-loss filter using air as dielectric loss free materials may be easily achieved, and a device face of MMIC may be protected without any degradation. In addition, a low-loss filter and MMIC may be easily connected.
Using a millimeter wave module manufactured in accordance with the above simple method, an inexpensive radio apparatus may be achieved.